Partially purified maize wallaby ear virus (MWEV) preparations were shown to contain 10 double-stranded (ds) RNA segments. Electrophoretic mobilities of the dsRNAs of MWEV and of other phytoreoviruses have been compared in two buffers. The total genome molecular weight of maize wallaby ear virus was ∼18.92 × 10 and ∼19.33 × 10 in PTE and Loening's buffer, respectively. Extracts from the virus-free leafhopper vector, , contained two dsRNA segments of molecular weight 1.15 × 10 and 1.08 × 10 in PTE buffer. Extracts from viruliferous insects also contained these same 2 dsRNA segments in addition to the 10 segments of maize wallaby ear virus. The electrophoretic pattern of dsRNA components of maize wallaby ear virus was similar to those of maize rough dwarf virus and Fiji disease virus suggesting a relationship between them. The degrees of relationship among these viruses and rice black-streaked dwarf virus, wound tumor virus, and rice dwarf virus were indicated by the electrophoretic patterns of their genome segments in the two buffers.